With the rapidly developed information technologies, computer has become one of many prerequisite electronic products in people's daily life. Computers are used in word processing, storage and processing of video files, audio files, multimedia files, and other important digital data, etc. In general, a computer is equipped with a hard disk drive, a compact disk drive, a floppy disk drive, etc. for reading and storing data. A computer can also be connected to various portable storage devices, such as portable hard disks, USB flash disks, etc., so that data in the computer can be stored on the portable storage device for use at different places.
A portable storage device generally has a universal serial bus (USB) plug as a transmission interface. In use, the USB plug can be directly plugged in a USB connector on a computer case to achieve the effect of Plug and Play for data transmission. Accordingly, with the USB interface, a user can conveniently use the portable storage device. However, due to the Plug and Play effect of the USB interface, even an unauthorized user can freely download all data stored in the computer with any portable storage device. Therefore, personal or private data stored in the computer are dangerously subject to stealing and illegally disclosure.